There is a need in the art for a low cost, high strength, high performance steel composition. Such high strength, high performance steels have various applications in both the commercial and military industries. For example, commercial applications of high strength, high performance steels include the following: pressure vessels; hydraulic and mechanical press components; commercial aircraft frame and landing gear components; locomotive, automotive, and truck components, including die block steels for manufacturing of components; and bridge structural members. Exemplary military application of high strength, high performance steels include hard target penetrator warhead cases, missile components including frames, motors, and ordnance components including gun components, armor plating, military aircraft frame and landing gear components. In particular, there is a need for steels that are capable of maintaining strength and toughness across relatively thick (e.g., >2″) sections.
One major disadvantage to traditional high strength, high performance steels is the relatively high cost of the steel, which arises from the alloy content, as well as the expensive manufacturing processes associated with such high performance steels. To produce high strength steel, prior art compositions generally contain high levels of nickel, tungsten, and/or cobalt, which are relatively expensive elements and contribute to the high overall cost of the final steel product.
For example, to produce strength and toughness combinations, traditional steels often contain significant amounts of nickel and cobalt, often totaling more than 15% of the alloy combinations. Other alloy steels contain difficult to process alloy additions, such as tungsten. One prior art composition, commonly designated as Eglin Steel and described in U.S. Pat. No. 7,537,727, contains up to 3.25% tungsten, which is expensive, limited in supply, and difficult to process due to the high melting point and very high density of the master alloy. The propensity of Eglin Steel to form detrimental, stable, tungsten containing carbides also makes the material difficult and expensive to process. The addition of tungsten also complicates waste stream/recycling capability of the alloy. Another prior art composition, commonly designated as AF-1410 and described in U.S. Pat. No. 4,076,525, provides a high strength, high performance steel at an expensive cost due to the high weight percentage of nickel, which contains 10% nickel as well as about 14% cobalt to achieve the desired high performance metrics. Another alloy composition, described in U.S. Patent Appl. Publ. No. 2010/0018613, provides a high strength, high toughness FeCuNiCr alloy steel that includes 0.35% to 0.55% carbon, 0.5% to 0.6% copper, 3.5% to 7.0% nickel, and 0.75% to 2.0% chromium, as well as requiring specific weight ratios of silicon (Si), copper (Cu), vanadium (V), and niobium (Nb) that satisfy a specified formula:2(% Si+% Cu)/(% V+5/9×% (Nb)≤14.
However, these prior art alloys are too cost-prohibitive to be used and manufactured on the scale required for penetrating weapons. In some cases, high-strength, high toughness steels are very difficult to process in thick sections. In view of the foregoing, a need exists for a high performance alloy steel composition that meets rigorous physical requirements and is easy and/or inexpensive to process.